Field of the Invention
This invention is for use as a relatively simple communication system for establishing a communication link between a central station and a number of remote stations. For example, it can be used in security alarm systems where a central station can call upon a number of unattended remote locations to take some action, if necessary, or the security status of each remote location can be polled or inquired into. For example, a number of unattended stations may have fire detection devices and the status of the fire detecting devices can be continuously monitored. If the device detects a fire, this is communicated to the central station which can then call that station to turn on an alarm or a sprinkling system or the like.
The system is not intended to carry on a sophisticated transfer of information and intelligence between the central station and the remote receiver stations. It is basically designed and constructed to operate so that the remote station will recognize when it is being called or polled and will send back a signal indication indicating its status, if it is being polled, or if being called, will recognize that fact and will respond by taking some prearranged action. As another example, a farm or ranch might have a sprinkling system and the operator might want to turn on sprinklers selectively at different locations. Also, the system might be equipped with devices which sense the moisture level at each remote station and when the station is polled and the moisture has reached a prescribed level, it returns a signal to indicate the moisture level and an operator or automatic controller can then turn off the sprinkler at that location.